Establishment and Molecular Characterization of an In Vitro Model for PARPi-Resistant Ovarian Cancer

Area of Science:

• Oncology
• Molecular Biology
• Drug Resistance

Background:

• Acquired resistance to Poly (ADP-ribose) polymerase inhibitors (PARPi) is a significant clinical challenge.
• Understanding resistance mechanisms in both BRCA1-proficient and BRCA1-deficient backgrounds is essential for effective cancer therapy.

Purpose of the Study:

• To establish and characterize in vitro models of acquired PARPi resistance.
• To investigate the role of multidrug resistance (MDR) and ABC-transporter activity in PARPi resistance.
• To compare resistance mechanisms in BRCA1-proficient versus BRCA1-deficient cells.

Main Methods:

• Long-term olaparib exposure to derive PARPi-resistant cell lines from isogenic backgrounds.
• Assessment of cross-resistance to other PARPis and chemotherapeutics.
• Drug efflux inhibitor sensitivity assays (verapamil, diphenhydramine).
• PARP-trapping activity assays.
• Dual-fluorescence co-culture experiments to study clonal dynamics.
• Inhibition of Multidrug Resistance-associated Protein 1 (MRP1) with MK-751.

Main Results:

• PARPi-resistant cells exhibited cross-resistance to other PARPis and reduced susceptibility to cisplatin adduct formation.
• PARPi resistance was associated with reduced PARP-trapping activity and increased MDR protein activity.
• BRCA1-proficient and BRCA1-deficient models showed distinct ABC-transporter expression profiles and cross-resistance patterns.
• PARPi-resistant cells outcompeted sensitive cells under olaparib selection, a phenomenon mitigated by an MRP1 inhibitor.

Conclusions:

• Established in vitro models facilitate the study of PARPi resistance mechanisms in HR-proficient versus HR-deficient contexts.
• Multidrug resistance and altered drug efflux play critical roles in acquired PARPi resistance.
• These models can aid in developing novel strategies, including drug efflux pump inhibitors, to overcome PARPi resistance.